Chernobyl (place)

On April 26, 1986, Reactor #4 exploded and caught fire. This is, as many of you know, very bad. Not many of you are likely to know quite how bad that is, exactly, so let me try to paint a picture for you.

Late one night, some guys down at the control room, who were in charge of shutting down the reactor (for routine maintenance), decided to perform a "test." They were curious: what would happen if they turned off the emergency core cooling system, and then turned off the power to the reactor? Would there be enough juice latent in the circuit to power the main cooling system long enough to complete a shutdown? Would aliens make contact? Would Lenin rise from the dead and give them a medal?

Not to be daunted by having not really discussed the procedure they were about to perform with their colleagues in operations, let alone the variety of intervening safety regulations, they proceeded to find out.

They started to turn down the supply power and fiddle with the reactor output. They had a little trouble with this: rather than stabilize the reactor at 1,000 MW prior to shutdown, they (doh) realized they'd let the pesky little sucker drop all the way down to 30 MW. That's 30. So they freed the reactor control rods manually and tried to correct it and move on. Unfortunately, now the reactor's last breath - which was supposed to power the shutdown, had already gasped. Fluid pressure up, steam pressure down. Things were moving too quickly. So what did they do?

They yanked all the rods out of the core and cranked down the feedwater flow.

That sort of solved their steam problem, but it made their reactor a teensy bit unstable. Unfortunately, as they'd turned off primary power and disabled the emergency cooling system, the reactor's turbines were powering its own cooling pumps. This was a rather "delicate situation", since the pumps, the steam pressure, the reaction, and the turbines, are all, well, related. Should the turbine slow, the cooling would slow, things would get hot. That might speed up the turbine again, of course, and get things cooled off again. But the engineers - in addition to the plant's architects - had not been sufficiently aware of the problem with steam.

The problem with steam is that it isn't nearly as efficient a coolant as water, and in addition, steam doesn't really absorb that many neutrons compared to water (absorbing neutrons would help “moderate” a nuclear reaction).

You can probably see where this is going, right? More heat, more steam, more reaction, more heat, more steam, etc. etc. This is what engineers working on RBMK Reactors like to call a "positive void coefficient."

And what happened at Chernobyl, basically, at the end of all this confusing mess, is that the engineers found themselves with the rods out of the reactor and all of the relevant cooling systems disabled. Their coolant boiled. Oh, they got their steam pressure then, alright. A few hundred times design capacity.

Then the core exploded.

They also got bonus extra credit science lab points for experimentally verifying the fact that, yes, graphite reactor shielding will burn, if you get it hot enough. In fact, once you get it going, it's damn hard to put out.

Many of you already know this, or some abbreviated version of it. You probably also know that the irradiated cloud of smoke, steam, and dust that rose from the site afterwards spread over the entire Ukraine, Russia and Belarus, and then eventually most of Europe. Principally, the worst contaminants in the cloud were Cesium 137, Iodine 131, and Strontium 90. Iodine and Strontium, in case you didn't know, like to collect inside the human body in various places where it's impossible to get them out. They also have nice, long half-lifes.

In the words of the Associated Press, "The Kremlin tried to conceal the accident and delayed evacuation of people from nearby towns for days. Firefighters and other workers who were the first at the destroyed reactor had little or no protection from radiation."

Well, you can probably see where this is going. Now let's start talking about the things you are less likely to know. The news, usually so reliable for a good horror story, has been remarkably silent on this topic over the intervening years. Perhaps they realized that some news is so bad, it’s bad for ratings.

The radiation release, by the estimate of the DOE task force assigned to the incident, peaked at 1900 PBq - or roughly 400 times the amount of radiation released by the atomic bomb dropped on Hiroshima. Most of the trees and small animals within 6 miles of the plant died almost immediately.

More than 4,000 of the workers assigned to the cleanup of the disaster are dead. Another 70,000 have been "disabled" by radiation.

About 3.4 million people (the population of the Ukraine is roughly 50 million in all), including over a million children, are considered "affected" by Chernobyl. Thyroid cancer, for instance, has become remarkably common - that's that pesky iodine. It has a tendency to get in everything. Italians were finding it in their breast milk a year after the accident. Of course, there is mounting medical evidence of numerous unanticipated effects both on humans at various levels of exposure, as well as the regional ecology, making the overall picture substantially worse than originally anticipated.

Reactor number four (which represents, collectively, about 170 tons of radioactive waste) is now encased in concrete. Reporters like to call it "the sarcophagus."

However, we can hardly blame the construction crew for rushing the job a bit. An estimated 10% of the surface of the shielding displays cracks; overall, several experts have warned of imminent structural failure in the container. This would, of course, be a fresh catastrophe. Reactor number two was shut down in 1991 following a fire, while number one was closed in 1996 as part of a desperately brokered deal with a coalition of European governments, following a series of serious, related “incidents” on site. Reactor number three (no exception to its siblings, with over two dozen safety-related shutdowns in the past decade) continued to operate until it was shut down permanently today, on December 15, 2000. The cleanup of this reactor alone is estimated to take over a decade. And you should hear what their idea of a "cleanup" is.

Chernobyl is the worst disaster in the history of nuclear power generation, but it is not the worst nuclear disaster in the history of the former Soviet Union. Chelyabinsk, home of the Mayak nuclear weapons facility, situated near the scenic southern Ural Mountains, starting in about 1948, managed to contaminate almost 30,000 square kilometers, releasing more radiation in total than Chernobyl. They pulled this off through a strict regimen of intentional dumping of radioactive waste into the Techa River, an explosion at a nuclear waste storage tank in 1957, and a windstorm, which happened to pick up and spread radioactive sediments from the (seasonally) dry lakebed of Lake Karachay (they’d been dumping waste in it too – perhaps nominally smarter than dumping it in the river?).

An April 1993 explosion at a reprocessing facility in Seversk, Siberia, called “Tomsk-7” – another marvel of Soviet atomic safety practices (can you say open cooling system?) – resulted in the release of 4.3 TBq (115 Ci) in long-lived isotopes – maybe around 500 grams of plutonium, along with a few other goodies like uranium, niobium, zirconium and ruthenium – over an area of approximately 120 square kilometers. It was not the first major accident at the facility, either… there was that howler back in ’81, when an engineer lost both his arms attempting to place three capsules of weapons grade plutonium inside a container designed to hold only one. Oops – critical mass! Really folks, I’m just getting warmed up. I could go on for hours.